The invention relates to a centrifugal separator of vertical axis for the separation of a flowable medium, in particular a dental liquid/solids mixture, from conveying suction air, having a motor-driven removal element, which is arranged in a flow chamber which has a rotationally symmetrical peripheral wall and a bottom limit, and in which a top, central outlet for the suction air and a bottom, peripheral outlet for the flowable medium are flow-connected to an inlet for the mixture to be separated, which opens out between these two outlets, the peripheral outlet being surrounded by an annular non-return valve, and vanes being provided on the removal element between the mixture inlet and the outlet.
A centrifugal separator of this nature is known, for example, from WO 94/18903. The centrifugal separator has a driven removal element, which essentially forms a pump impeller by means of which the air flow is sucked from the outside inward, i.e. in the opposite direction to the centrifugal forces, over at least one separation edge. The pump impeller has planar, radial vanes which convey the flowable medium outward into the peripheral outlet and force it through the non-return valve. The vanes, which extend all the way to the central outlet for the suction air, also remove residues of the medium from the suction air, so that it enters the outlet which is in communication with an external extraction device in a dry state.
The flow chamber through the removal element is delimited at the top and bottom by rotary parts, the axial distance between which is shortest at the peripheral outlet and becomes greater toward the hub, i.e. as the radius becomes smaller. The surface area of the blades is to be as large as possible, in order, on the one hand, to optimize the separation of the flowable medium from the suction air and, on the other hand, to optimize the way in which it is discharged into the peripheral outlet. However, the number of blades is limited, since the flow chamber must as far as possible not be restricted in the area close to the hub. Although a convex shaping of the base plate does increase the cross section of flow, it forms, since the drive shaft runs vertically, a sump in which residues of the flowable medium accumulate when the removal element is switched off.
The invention is therefore based on the object, in a centrifugal separator of the type described in the introduction, of bringing the mixture which is to be separated into contact with a vane surface area which is as large as possible while neither impairing the flow chamber nor promoting accumulation of residues in the flow chamber.
According to the invention, this is achieved by the fact that the mixture inlet is formed between the bottom edge of the peripheral wall and a holding ring for the non-return valve.
In this way, the mixture inlet, which is preferably annular, is arranged as far as possible toward the outside of the removal element, directly in front of the peripheral outlet, where the peripheral speed of the vanes is correspondingly high. The mixture comes into contact with the removal element from above, and the centrifugal force means that mixture fractions are thrown outward from the vanes and are forced through the outlet and the annular non-return valve. Since the pressure reduction from the suction machine is active at the central outlet for the suction air, the air is diverted inward around the bottom edge of the peripheral wall, entraining mixture fractions. To avoid the accumulation of mixture residues in the removal element when the drive of the removal element is switched off, it is preferable for the bottom limit of the flow chamber to drop down toward the peripheral outlet for the medium below the mixture inlet or for the removal element to be provided with a bottom base plate which has an inner surface which drops down toward the peripheral outlet.
Shaping the bottom limit in this way on the one hand improves the discharge of mixture to the outside but, on the other hand, also reduces the cross-sectional area of the flow chamber, so that, if it is necessary to ensure that no mixture residues can be entrained through the central suction-air outlet, it is necessary to provide sufficient height for the flow chamber, in which the volumes of components which are absolutely necessary are made as small as possible and their surface areas which are active in the separation as large as possible. Therefore, in a further preferred embodiment, the removal element has a hub which is provided only in the lower part of the height of the removal element, and first blades connected to the hub are provided, which first blades are connected to a top guide element and/or to a bottom base plate and the outer ends of which blades form vanes. The shortened hub leaves the central space below the suction-air outlet clear, and the number of first blades connected to the hub is small, for example six. Since, as mentioned, the active surface area inside the removal element is also to be large, in a further preferred embodiment in each case a second blade which is at a radial distance from the hub and the outer end of which forms a further vane is arranged between in each case two first blades which are connected to the hub. The separating effect is improved still further if in each case a third blade, which is at a greater radial distance from the hub and the outer end of which forms a further vane, is arranged between in each case a first blade, which is connected to the hub, and a second blade, which is at a distance from the hub. Therefore, in order, on the one hand, to optimize the separation of the flowable medium from the suction air and, on the other hand, the way in which it is discharged into the peripheral outlet, groups of blades are provided, the group of first blades running through the entire flow chamber from the outside inward, the group of second blades being arranged in the spaces between the first vanes but extending only sufficiently far inward for an adequate passage to remain clear between the first blades, and the additional group of third blades which is preferred being arranged in the peripheral region of the removal element, in each case in the space between a first blade and a second blade. The second and third blades, which are not connected to the hub, are attached to the top guide element and/or to the bottom base plate.
In the abovementioned exemplary embodiment with six first blades, the preferably three groups of blades result in a total of 24 vanes which project into the mixture outlet all the way to the non-return valve.